Southern African palaeoclimates and variability : the story from stalagmites, pollen and coral.

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Abstract

Compared to extensive study in the northern hemisphere, very little is known of southern
African palaeoclimates. This study aimed to extend understanding of the nature of and
controls on southern African palaeoclimates of the last 40 000 years. Through a study of
the approximately 20 000 year long Makapansgat and Wonderkrater palaeoclimatic
records, and an extensive literature review of southern African palaeoclimatic studies, a
number of common rainfall and temperature fluctuations were detected across the summer
rainfall region. Based on these trends, general models of rainfall and temperature changes
over time were developed for the region. The analysis of a coral core, derived from a
Porites lutea head from Sodwana Bay, covering the last 116 years, indicated higher
frequency climatic fluctuations over the last century. Climatic variability on the long- and
short-term could then be related to known atmospheric processes through application of the
Tyson (1986) model for southern Africa atmospheric circulation. North-south shifts in
mean circulation dominate climatic variability in the region but there are also regular
disturbances to this mean, such as in the form of the EI Nino - Southern Oscillation.
The fluctuations seen in present and palaeoclimatic records are the result of a complex
interaction between internal and external mechanisms of climate change. Wavelet analyses
of recorded and proxy climatic datasets highlighted the cycles which dominate southern
African climatic variability on timescales from years to millennia. The causes of these
cycles were then assessed in the context of established solar, atmospheric and oceanic
models. Wavelet analyses also provided an indication of frequency changes over time and
were therefore useful for detecting climate change. An analysis of proxy and recorded
climatic datasets for southern African rainfall over the last 100 years indicated a frequency
modulation of the 18 year rainfall cycle, which was first described by Tyson (1971). This
variation may be related to anthropogenic climate change.
It became apparent from this study that there is a need for increased scientific interest in
the palaeoclimatic trends of the region. The number of continuous, high-resolution datasets
needs to be increased to allow for comparison and confirmation of various trends with
records from sites across the globe. An understanding of the nature of regional and global
teleconnections is essential before reliable climate change models can be established.
There is also a need for further understanding of short-term southern African climate variability on inter-annual timescales.It is only once we have an understanding of the natural climatic variability of the region ,and its inherent cyclicity,that we can begin to distinguish the impact of anthropogenic activities on climate.